C. H. Pua

Graphene-based Q-switched pulsed fiber laser in a linear configuration

A pulsed laser system is realized with graphene employed as a Q-switch. The graphene is exfoliated from its solution using an optical deposition and the optical tweezer effect. A fiber ferrule that already has the graphene deposited on it is inserted into an erbium-ytterbium laser (EYL) system with linear cavity configuration. We successfully demonstrate a pulsed EYL with a pulse duration of approximately 5.9 \mu s and a repetition rate of 20.0 kHz.

Photonic crystal fiber based dual-wavelength Q-switched fiber laser using graphene oxide as a saturable absorber

A Q-switched dual-wavelength fiber laser with narrow channel spacing is proposed and demonstrated. The fiber laser is built around a 3 m long erbium doped fiber as the gain medium and a 10 cm long photonic crystal fiber (PCF) as the element used to generate the dual-wavelength output. The PCF has a solid core approximately 4.37 μm in diameter and is surrounded by microscopic air-holes with a diameter of about 5.06 μm each as well as a zero-dispersion wavelength of about 980 nm. A graphene oxide based saturable absorber is used to generate the desired pulsed output. At the maximum pump power of 72 mW the laser is capable of generating pulses with a repetition rate and pulse-width of 31.0 kHz and 7.0 μs, respectively, as well as an average output power and pulse energy of 0.086 mW and 2.8 nJ, respectively. The proposed fiber laser has substantial potential for use in applications that require longer duration pulsed outputs such as in range finding and terahertz radiation generation.

Narrow Spacing Dual-Wavelength Fiber Laser Based on Polarization Dependent Loss Control

By controlling the polarization state of a simple ring erbium-doped fiber laser with photonics crystal fiber, polarization controller (PC) and tunable band-pass filter, this paper demonstrates stable operation of narrow spacing dual-wavelength fiber laser (DWFL). The flexibility of the tunable band-pass filter and PC allows the spacing tuning of the DWFL from 80 pm up to 600 pm. Such tuning ability offers flexibility in the application of DWFL, particularly in tunable microwave generation and radio over fiber. Throughout the experiment, the DWFL shows high power stability within 0.6 dB and wavelength shift of less than 10 pm. In addition to that, it also produces a narrow linewidth optical output of 3 pm with a high signal to noise ratio of more than 60 dB.

Graphene oxide-based waveguide polariser: from thin film to quasi-bulk

We have demonstrated a broadband waveguide polariser with high extinction ratio on a polymer optical waveguide coated with graphene oxide via the drop-casting method. The highest extinction ratio of nearly 40 dB is measured at 1590 nm, with a variation of 4.5 dB across a wavelength range from 1530 nm to 1630 nm, a ratio that is (to our knowledge) the highest reported for graphene-based waveguide polarisers to date. This result is achieved with a graphene oxide coating length along the propagation direction of only 1.3 mm and a bulk film thickness of 2.0 µm. The underlying principles of the strongly polarisation dependent propagation loss demonstrated have been studied and are attributed to the anisotropic complex dielectric function of graphene oxide bulk film.

Thermal Regeneration in Etched-Core Fiber Bragg Grating

Thermal regeneration is observed in etched-core fiber Bragg gratings (FBGs) with a fiber diameter of 5.6 μm. Etched-core FBGs are prepared by chemical etching using a hydrofluoric acid solution. Annealing is applied for all gratings to induce thermal regeneration. Thermal regeneration of FBG is observed at 680°C. The temperature sensitivity of regenerated etched-core FBGs is measured to be 13.9 pm/°C for a temperature range between 25°C and 700°C. With its high temperature resistance and large evanescent field interaction with its surrounding, thermally regenerated etched-core FBG has potential applications in high temperature sensing.

Tunable microwave output over a wide RF region generated by an optical dual-wavelength fiber laser

The dual-wavelength fiber laser provides a compact, robust and stable platform for the generation of microwave signals. Two approaches towards generating microwave emissions using dual wavelengths are explored in this work, with both exploiting the heterodyning beat technique. Both approaches are based on a ring fiber laser with an erbium-doped fiber, having absorption coefficients of 16.0?20.0?dBm at 1531?nm and 11.0?13.0?dBm at 980?nm, serving as the active gain medium. A 10?cm long photonic crystal fiber with a solid core diameter of 4.37??m and surrounded by air holes of 5.06??m diameter with a separation of 5.52??m between them serves to create the desired dual-wavelength output. A tunable band pass filter with bandwidth of 0.8?nm serves as a tuning mechanism together with a polarization controller. Channel spacings as narrow as 0.00043?nm can be realized, giving a microwave output of about 671.9?MHz. Furthermore, the channel spacing can be extended to as large as 0.03631?nm, giving a microwave emission in excess of 4.59?GHz. The output is highly stable, with little change in power or wavelength observed over a test period of 22?min.

Tunable high power fiber laser using an AWG as the tuning element

In this paper, a design of a High Power Tunable Fiber Laser (HP-TFL) in C-band region from 1536.7 to 1548.6 nm is set forth with Erbium Doped Fibers (EDFs) being used as a seeding signal and a booster amplifier. With a 1 × 16 channels Arrayed Waveguide Grating (AWG), this setup is capable of generating 16 different wavelengths with an average output power of 20.7 dBm.

FIBER LOOP MIRROR FILTER WITH TWO-STAGE HIGH BIREFRINGENCE FIBERS

A flber loop mirror (FLM) with two-stage high birefrin- gence (Hi-Bi) flbers is theoretically and experimentally studied for var- ious rotation angles and Hi-Bi flber lengths. The experimental spectra are observed to be in good agreement with the theoretical spectra, ver- ifying our theoretical model. The wavelength interval of the comb fllter depends on the Hi-Bi flber lengths and rotation angles. By varying the rotation angle from 0 - to 90 - , a comb-like transmission spectrum with small wavelength spacing is evolving into an exotic but periodic trans- mission spectrum and eventually become a larger wavelength spacing transmission spectrum. The FLM is useful in many applications such wavelength division multiplexing power equalization and management, switchable multi-wavelength flber laser, optical switch and etc.

Dual-Wavelength Fiber Lasers for the Optical Generation of Microwave and Terahertz Radiation

This review describes the evolution of dual-wavelength fiber lasers (DWFLs), which provide a simple and cost-effective approach for the optical generation of microwave and terahertz (THz) radiation. The emphasis of this review is to trace the early development of DWFLs, including the issues and limitations faced by the various gain media right to the latest advancements in this field as well as their roles in generating the desired output. This review covers both the simple approaches of narrow-band filters and comb filters for microwave radiation generation, as well as the use of DWFLs with diethylaminosulfurtetrafluoride or LiNbO3 crystals for generating THz radiation.

A Polyaniline-Coated Integrated Microfiber Resonator for UV Detection

We present a UV detector based on an integrated microfiber resonator. In fabrication, a thin layer of polyaniline (PAni) is deposited on a ~1-mm-diameter microfiber ring resonator-the sensing region of the detector. Red shift is observed in the output spectrum when PAni is irradiated with a UV light with a peak wavelength at 365 nm. This phenomenon can be due to the high absorbance in the UV region and photothermal effect of PAni. The wavelength shift is linearly proportional to the UV light intensity and the measured sensitivity is 6.61 nm/(W·cm-2).